The Northern Waters are mentioned twice in episodes of DreamWorks Dragons: The Series.
There is no description given of the Northern Waters. However, because they are 'North' it might be presumed that are cold. This watery area must also be marine and very deep to harbor giant squid and a current.
|“||Oh, that's pure squid ink, Hiccup. Wrestled from the colossal squid of the Northern waters.||”|
|— Johann in the "Dragon Flower"|
At the end of the episode, "Frozen", Trader Johann gives Hiccup a bottle of squid ink as a thank you for rescuing him.
|“||Oh, before you go, I have something for you. A little token of my appreciation. Pure squid ink, wrestled from the colossal squid of the Northern Waters. ... Ten summers ago, deep under the currents of the Northern Waters, I was staring directly into the black eye...||”|
|— Johann's story about he and the colossal squid in "Frozen"|
- It is possible that the Northern Waters might be synonymous with the Northlands or the Northern Territories.